1. Field of Invention
The present invention relates to a circuit and method for detecting the state of a switch and, more particularly, not by way of limitation, to a circuit for and method of detecting the state of a switch while reducing the current drain on a power source.
2. History of Related Art
It is well known in industries where cash and/or other valuables are stored in point-of-sale devices or containers accessible by the public that these containers may be susceptible to theft or break-in. Sometimes, it is not immediately evident that tampering has occurred. Other times, it may be useful to alert people in the area or the authorities that the tampering is taking place. For these reasons, tamper detectors have been developed. These detectors generally function by detecting the state of a switch using electrical circuitry. The switch is typically electromechanical in nature such that excessive tampering or movement of the associated container causes the switch to change electrical state. When a change of state of the switch is detected, a positive indication for tampering is given.
One such detector illustrated in FIG. 1 shows a discreet solution to detect a tamper condition. In FIG. 1, a switch 4 is normally closed, grounding a tamper pad 8 and discharging a static current from a battery 6 via a resistor R1. When tampering occurs, switch 4 opens, resistor R1 pulls tamper pad 8 to the positive terminal of the battery, and the static current from the battery 6 through resistor R1 will be cut off. The rise in voltage on tamper pad 8 is detected and utilized to indicate that a tamper has occurred.
One problem with detectors such as that illustrated in FIG. 1 is that the battery is continuously drained when the switch 4 is normally closed, thus shortening the battery life. This requires the battery to be changed periodically and increases the possibly that a dead battery may be in place at the time the item or container is tampered with. For the foregoing reasons, there is a need for a tamper detection circuit or device that reduces the power drain on the battery, thus preserving the life of the battery.